The field of the invention is generally that of devices for the storage of liquids, and more specifically, to an improved shut-off valve for use in pumping liquid into a storage vessel that shuts off the delivery pump when the tank becomes full.
Proper storage and handling of waste liquids, especially toxic liquids, has become very important because of the discovery that so many of them have been found to cause cancer and other serious diseases. Liquids that previously were treated as mere waste are now known to be highly dangerous to humans, as well as to the environment, and require careful and safe storage until they can be rendered harmless by further processing or become benign by passage of time.
The need to store these materials in leak-proof containers is now required by such government agencies as OSHA (Occupational Health and Safety Agency), the National Health Institute and Others. A wide array of storage containers may be used, from small 1 and 2 gallon cans to large tanks, both underground and transportable. A container widely used in this situation is a drum or holding tank; drums are quite plentiful and its thick metal walls will safely store most materials.
These tanks, along with other such containers, contain a standard, 2 inch diameter threaded aperture in the lid known as a "bung hole" that can be used for pouring or pumping liquid into the drum as well as to have test probes inserted thereinto for the purpose of determining various attributes of the stored liquid. This same bung-hole type opening is also found in virtually all storage tanks from the very small to the extremely large. The rim of the bung hole usually contains a series of threads to accept a threaded plug known as a "bung".
One disadvantage in the use of storage tanks and drums, is that they are so well sealed no light can penetrate the interior. In many cases no incandescent lamp can be safely used to aid one looking inside because the stored contents are either poisonous or highly combustible. Often the drum is pumped completely full of liquid and the pump is not shut down soon enough with the result that liquid spills out of the lid openings over the sides and onto the ground or other supporting surface to cause the toxic condition to become a problem all over again. Positioning a person to continually observe the level of fullness in the tanks raises labor costs and places him or her in a dangerous position near the toxic material.
Many of these valves are used in the automotive quick oil change service stations. Here, oil is removed from a vehicle and stored in a pit tank. Then oil is pumped from the pit tank to a large holding tank on the ground floor. The holding tank has a shut off valve when it is near full and shuts off the pump in the pit area. A disposal company is called and a truck is sent to remove the oil from the holding tank. If or when the valve on the holding tank sticks or fails, an oil spill is inevitable.
The prior art has tried to deal with the problem of shutting off the flow of liquid into a tank, when the level reaches the uppermost safe point, but such attempts have not met with success.
U.S. Pat. No. 5,007,450 (Add-on Liquid Overflow Shut-Off Valve for Tank) describes a portable device for stopping delivery to a tank when the liquid reaches a preset level. This patented valve is complex, costly, is inefficient due to air leakage, can stick, wear, and cannot easily be checked to see if it is working properly.
The present invention solves these problems by providing a pressure valve with a similar function, however, containing no floats that stick, has no moving parts in the liquid, no air leakage, and provides an easy way to check the valve to ensure that it is operating properly.